The present invention relates to a regeneration-type cryopump of the kind comprising a housing containing a pumping duct having a flange for connecting it to an enclosure to be evacuated, and condensing, sublimating and, where applicable, adsorption/desorption means for trapping gases cryogenically. Such cryopumps are used in association with a valve which is inserted between the flange of the pumping duct and the enclosure to be evacuated. The purpose of the valve is to permit total isolation in particular when the cryopump is being regenerated, this operation consisting, as is known, of heating the trapping means of the cryopump to enable the gases which have been trapped as condensed or adsorbed deposits to be withdrawn by an auxiliary pump after having been restored to the gaseous state.
It is known that valves which are sealed against high vacua are particularly complex and expensive, in particular because they have to be so produced as to be capable of being over-heated to a temperature of approximately 500.degree. C, which rules out the use of conventional sealing glands. In certain designs of cryopump for ultra-high vacua, it is important for the pumping duct to be of particularly large dimensions, e.g. as much as 500 millimeters or even more, in order to ensure that the gases coming from the enclosure to be pumped out have maximum access to the trapping means. The latter can thus be in the form of annular structure coaxial with the said pumping duct, this annular trapping structure having a wide central opening so as to be accessible to the gases for the whole of its extent. It will be appreciated that in particularly high performance designs of this kind the valve is a component of major importance, not only because of the isolating function which it performs but also because of its considerable size. Also, in view of this size, the presence of a valve between the cryopump and an enclosure to be evacuated results in a pressure loss which, even though small, results in a reduction in pumping efficiency.
It is an object of the present invention to provide a regeneration-type cryopump which incorporates within it the parts required to form a pseudo-valve in conjunction with the pumping duct, thus making it unnecessary to insert a valve body between the cryopump proper and the enclosure to be pumped out and enabling a direct connection to be made to the enclosure to be evacuated, at the same time as the trapping means remain perfectly accessible.
Another object of the invention is to provide such a cryopump which incorporates a pseudo-valve which can be over-heated to a temperature of 500.degree. C and yet which still provides a sufficiently good seal to allow the cryopump to be regenerated without having a serious effect on the level of vacuum reached in the enclosure to be evacuated.
A further object of the invention is to provide a cryopump of this kind which is impeccably sealed by simple means and yet which can be over-heated to a moderately high temperature such as one of the order of 150.degree. C.
Another object of the invention is to provide a cryopump of the kind having a pseudo-valve, which can be connected to the enclosure to be evacuated either by its top or its bottom.